1. Field of the Invention
The invention concerns a remotely operable sample-taking appliance, especially for ascertaining radio activity profiles (characteristics) in contaminated material surfaces and the chemical composition of strata close to the surface, wherein for each sample a layer of material is removed electrolytically from the surface region under investigation by means of a sensor containing an electrolyte-impregnated small sponge, and the removed material is absorbed in the sensor for a subsequent chemical analysis and/or of its radio-activity, in order to produce a radio-activity profile of the surface region from a plurality of successive samples; as well as a method of operating the sample-taking appliance.
2. Prior Art
For example, in nuclear reactor installations as the duration of operation continues component surfaces are increasingly contaminated by fission and activation products carried along by the cooling agent, and as a result of this contamination the servicing of the installation becomes ever more difficult as time goes on, until finally there is a danger of an unacceptably high radiation dosage being received in servicing, and in order to avoid this the installation must be decontaminated. On account of the magnitude of the surface to be decontaminated the decontamination of a reactor circuit system, for example, is an expensive project requiring detailed preparation so that the decontamination can be carried out in the minimum time with minimum possible radioactive fall-out and with an adequate certainty that the residual activity does not at any location exceed the permitted value after decontamination. For such a preparation adequate knowledge of the nature of the surface layer to be decontaminated is necessary and in particular essentially as regards the distribution of the contamination both over the surface and in the depth of the surface layer as well as the chemical composition of the surface layer. In general, the contamination is present either in a loose layer resting on the surface of the component which may easily be removed, for example, by rinsing or is chemically bonded in the material and/or diffused into the material at that region of the component which is close to the surface. In order to obtain the distribution in depth of the contamination the contaminated material can be removed layer-by-layer in a given surface region and the activity for the material of each removed layer can be determined. The activity plotted on a diagram against the layer depth results in an "active profile" of the examined surface region, from which the depth of the layer to be decontaminated can also be extrapolated to obtain the residual activity for the component. Various per se known methods may be used for the removal of the layers, but since the material to be removed may be relatively highly radioactive and the layers to be removed may be very thin, for example up to only a few .mu.m thick, a chemical, especially electrolytic, method of removal of material is preferable to mechanical removal of material, such as grinding, sand-blasting etc. For the electrolytic removal of radioactive material an electrode block lined with a small synthetic plastics sponge impregnated with electrolyte will advantageously be used, which forms an electrolytic cell with the material layer to be removed acting as a counter-electrode, the electrolysis being carried out in such a way that all material is contained in the sponge and can be analysed both chemically and as regards its activity. No particular difficulties arise here for the electrolysis itself, that is, in the selection of the actual electrolyte, for choice of the electrolytic current intensity, the magnitude and polarity of the cell voltage, etc., since comprehensive special literature is available.
An activity profile may of course be only evaluated usefully if it is taken from suitably satisfactory samples on the basis of sufficiently precise measured values, and in the sample-taking there is the additional difficulty that the material is radioactive and under some circumstances even relatively highly active, and thus remote operation must be provided for the sample-taking as well.